Small-medium scale heating (15 – 500kW)
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Equipment: For projects such as community halls, swimming pools, smaller commercial properties, hotels, nursing homes and small district heating schemes, pellet or wood chip boilers would be most appropriate.
As with domestic boilers, you will need a separate outbuilding to house the boiler, feed equipment and accumulator tanks (if needed), and separate fuel stores constructed. The boiler room and fuel store must be separate to comply with fire-safety regulations.
The capital costs of installations are higher than fossil fuel systems but running costs should be low compared to oil, LPG or electric heating. If a local source of woodchips is available within 20 miles or so then the price is of fuel is nearly as competitive as natural gas. Pellets are now available at less than the current oil price equivalent.
Fuel specification: when using wood chips, the greatest environmental and cost benefits come from burning locally sourced woodchips. It is vital to first of all to determine the quality and delivery options for woodchips in your area to ensure that the boiler you choose can use the local supply. Boilers at the smaller end of the output range usually require finer and drier wood chips than larger boilers with peak outputs of 100kW or more. Likewise, when planning the storage facilities, you need to know whether your supplier can deliver frequently or whether you will need to store larger quantities.
Pellets are a much more standardised form of fuel and delivery distances can be greater as it is a less bulky form of wood fuel than wood chips.
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Storage: If you are assured of a regular delivery of woodfuel every week or fortnight, then an outdoor hopper is usually the cheapest option. The supplier can load chips or pellets directly into the hopper; these are then automatically fed into the burner by an auger mechanism. The hopper needs to be accessible so that the chips or pellets can be tipped in from the delivery vehicle. Alternatively, the supplier may deliver wood fuel in bulk bags, which are lifted and emptied into the hopper by crane or tractor, but this is more time-consuming and costly. Access roads and ramps must be constructed to a standard suitable to take large tractors and trailers or tipper lorries.
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If regular deliveries cannot be assured then a larger storage facility will be needed such as a silo or storage barn. For rural projects where a tractor is available, a storage shed or barn would be ideal, as the hopper can be filled using a tractor front loader.
A cubic metre of pellets has roughly four times the calorific value of 1m3 of dry woodchips, therefore the storage requirements can be reduced or the frequency of deliveries can be reduced. Both these factors mean that pellet heating may be a better proposition for urban areas where space is at a premium and traffic needs to be reduced.